this is in image of the centre of the system, it is 6 times as big as the other fields spread over europe. The water around it has been made to keep wild animals from wandering around and knocking over antennas.

The frequency range of LOFAR is limited by the ionosphere - beyond the low end of their frequency range, the ionosphere is reflective, so they'd just see reflections from ham radio operators, radar systems, etc. Most radio astronomy takes place at somewhat higher frequencies - pulsars, for example, are often observed around the 1-1.5 GHz range. (There's a hydrogen emission line at 1.5 GHz, which lets you get a good look at the hydrogen gas in the universe, so many telescopes are designed to observe around that frequency.) Other telescopes go up to 100 GHz, or even higher, although radio waves at those frequencies start to be distorted by other atmospheric effects (humidity; turbulence), so the telescopes tend to be built at high altitude. (See, for example, ALMA [wikipedia.org].)